The present invention relates a ball screw and a method for assembling the same.
A ball screw used in a transfer mechanism, a fine positioning mechanism or the like is constituted by a screw shaft and a nut that is threadedly engaged therewith, and an outer peripheral face of the screw shaft and an inner peripheral face of the nut are provided with screw grooves in a spiral shape opposed to each other. Further, a plurality of balls are rollably charged into a ball rolling path in a spiral shape formed between the two screw grooves, and the screw shaft and the nut are made to be moved relative to each other in an axial direction via rolling of the plurality of balls.
In order to continue relative movement of the screw shaft and the nut, it is necessary to infinitely circulate the ball rolling in the ball rolling path. Therefore, the ball screw is provided with a ball return path for circulating the ball by delivering the ball from an end point to a start point of the ball rolling path. When the ball reaches the end point of the ball rolling path by turning around the screw shaft by a plurality of times while moving in the ball rolling path, the ball is moved from one end portion of the ball return path into the ball return path, passes in the ball return path and is returned from other end portion of the ball return path to the start point of the ball rolling path.
At the end point and the start point of the ball rolling path, the ball is moved between the ball rolling path and the ball return path and in order to smoothly move the ball, there are arranged ball guide members for guiding to move the ball at the end point and the start point of the ball rolling path. Further, the ball guide members are fixed to the nut by various methods.
For example, Japanese Utility Model Number 3034052 describes a ball screw in which a ball guide member is fixed by a spring ring.
However, according to the ball screw described in Japanese Utility Model Number 3034052, an area of bringing the ball guide member into contact with the spring ring constituting a fixing member is small and therefore, when a ball is clogged in a ball rolling path or a ball return path in high acceleration or deceleration or under high load, there is a concern of destructing the spring ring by the ball guide member pressed by the ball.
Further, it is necessary to form a groove having a section in a taper shape for fitting the spring ring to fix to a nut at an inner peripheral face of the nut and therefore, there is a difficulty in machining the nut. Further, in fabricating (integrating) the ball screw, there poses a problem that it is not easy to attach the spring ring to the nut without rattle, or attaching the spring ring thereto by applying a uniform pressure over an entire periphery of the spring ring.
Hence, it is a problem of the invention to resolve the above-described problem provided to the ball screw of the background art and provide a ball screw which is difficult to be broken and easy to fabricate.